Klebsiella is a genus of Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule.

Klebsiella bacteria tend to be rounder and thicker than other members of the family Enterobacteriaceae.

[6] Members of the genus produce a prominent capsule, or slime layer, which can be used for serologic identification, but molecular serotyping may replace this method.

[8] Members of the genus Klebsiella typically express two types of antigens on their cell surfaces.

[6] Klebsiella species are known to also infect a variety of other animals, both as normal flora and opportunistic pathogens.

Drug-resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high-impact medical areas such as intensive care units.

[15] The ability of K. pneumoniae to colonize the hospital environment, including carpeting, sinks, flowers, and various surfaces, as well as the skin of patients and hospital staff, has been identified as a major factor in the spread of hospital-acquired infections.

[21] Additionally, K. variicola is known to associate with a number of different plants including banana trees,[22] sugarcane[23] and has been isolated from the fungal gardens of leaf-cutter ants.